1. Field of the Invention
The present invention relates to a control system for an internal combustion engine in which compression ignition is performed, and particularly to a control system for controlling an amount of fuel injected during a pilot injection of fuel that is performed before a main injection of fuel.
2. Description of the Related Art
Japanese Patent Publication No. 3572435 (JP '435) discloses a control system for an internal combustion engine that estimates a compression end temperature that is a temperature of an air-fuel mixture in a cylinder when a piston is positioned at a compression top dead center. The control system disclosed by JP '435 increases the pilot injection amount of fuel when the estimated compression end temperature becomes relatively high. The control system of JP '435 suppresses a combustion noise by increasing the pilot injection amount of fuel in a high-load operating condition of an engine.
The ignitionability of fuel in the compression-ignition internal combustion engine depends on the compression end temperature during a low temperature condition, e.g., immediately after the cold start of the engine, or in a low load operating condition immediately after starting the engine. If similar control for a high load operating condition is attempted by the control system taught by JP '435, as in the low temperature condition or in the low load operating condition, the ignitionability of fuel is known to degrade.